During the relative longitudinal displacement between the profiled sleeve and the profiled journal, the balls roll in the first or outer and the second or inner ball grooves in a substantially friction-free way, so that the balls and thus the ball cage cover a total of half the displacement path between the profiled sleeve and the profiled journal. The longitudinal plunging unit thus permits a low-friction change in length of the shaft assembly.
It is necessary to delimit the displacement path of the ball cage by the spaced axial stops in order to avoid the ball cage from leaving the ball grooves. Even if, as a result of a ball groove run-out delimiting the ball grooves, the ball cage cannot run out as mentioned, it is essential to provide an axial stop so that the balls of the ball cage do not abut the ball groove run-out, which would result in a self-inhibiting effect.
From U.S. Pat. No. 6,306,045, it is known to work a first annular groove into the profiled sleeve at its end facing the profiled journal and, with axial distance therefrom, to work a second annular groove into the profiled sleeve, wherein in each first and second annular groove a securing ring is inserted, which securing rings form axial stops for the ball cage which is axially displaceable between said stops.
From U.S. Pat. No. 6,902,487, it is known to provide an annular stop member at the end of the profiled sleeve facing the profiled journal next to the securing ring, wherein the stop member is arranged radially between the profiled sleeve and the profiled journal. For assembly purposes, the stop member is inserted into the profiled sleeve. It form-fittingly engages the ball grooves and, by means of one end, is supported on a conical portion of the profiled sleeve, whereas the other end serves as a stop face for the ball cage. Producing such a stop member is complicated and expensive because its cross-sectional profile corresponds to the ball grooves. Furthermore, the stop member can be introduced into the sleeve in certain rotational angular positions only as otherwise it would not be able to engage the longitudinally extending ball grooves.
DE 296 11 785 U1 shows a longitudinal plunging unit with a profiled journal, a profiled sleeve and balls which are held therebetween in ball grooves and which are accommodated in a ball cage. At its free end which enters the profiled sleeve, the profiled journal comprises a stop plate against which the ball cage is able to abut. At the attaching end, the displacement path of the balls is delimited by the ball groove run-out.
U.S. Pat. No. 3,365,914 proposes a rotational coupling having an outer part and an inner part between which, in tracks, rollers are held in a ball cage for torque transmitting purposes. The displacement path of the ball cage is delimited by a shoulder in the outer part on the one hand and by a cover connected to the outer part on the other hand.
U.S. Pat. No. 6,802,781 shows a longitudinal plunging unit wherein the ball cage is able to abut the ball groove run-outs in order to delimit the displacement path.
U.S. Pat. No. 6,705,948 proposes a longitudinal plunging unit wherein the ball cage is able, in both directions, to abut securing rings positioned in annular grooves in the profiled journal. As already mentioned in connection with the profiled sleeve referred to above, the annular grooves are arranged in the region of the ball grooves and, respectively, in the region of the ball groove run-outs. When producing the annular grooves in a turning operation, this leads to an interrupted cut as a result of which the tools are subjected to an increase in wear. Furthermore, prior to producing the annular grooves, the components are usually hardened to prevent the formation of burr in the region of the ball grooves, which, in turn, leads to a further increase in tool wear, with the tool service life being reduced further and with the production costs being increased.